Typically, a fuel tank made of an iron plate has been the mainstream of a fuel tank mounted in a passenger vehicle or the like. In recent years, however, the number of fuel tanks made of resin is increasing from the viewpoints of weight reduction, rust prevention, ease of molding, and the like. The blow molding method that is easy to mold hollow bodies is heavily used for the production of resin fuel tanks. A tubular parison formed by melting down thermoplastic resin is extruded. Air is then blown into the parison held by a mold for molding. Accordingly, a molded part of a desired shape can be obtained.
Generally, a protrusion protruding outward is formed on a fuel tank in the blow molding process. An opening is formed in the protrusion in the subsequent fabrication process. A lid member to which a functional component such as a fuel pump is fixed is mounted on the protrusion. An oil-tight sealing is provided between the protrusion and the lid member to prevent fuel or gas from leaking from the opening when the lid member is mounted on the protrusion.
An example of such a seal structure is disclosed (Patent Literature 1). In this example, the lid member includes a tubular portion accommodated in an opening portion, an outer flange portion that closes an upper end of the tubular portion and projects from the tubular portion toward the outer periphery, and a sealing member mounting portion extending downward from an outer end of the outer flange portion, on which a ring-shaped sealing member is mounted. A flanged sleeve includes a sleeve portion in intimate contact with a neck portion, and an inner flange portion whose lower end of the sleeve portion projects toward the outer periphery to be in intimate contact with an inner wall of a tank body. The flanged sleeve is made of a resin with higher heat resistance than a resin forming the tank body. The tubular portion is accommodated inside the sleeve portion when the opening portion is blocked with the lid member. The outer flange portion comes into contact with upper ends of the neck portion and the sleeve portion to bring an inner peripheral side of the sealing member into intimate contact with an outer peripheral side of the neck portion. In Patent Literature 1, such a seal structure is adopted to eliminate the need of a fastening structure such as a screw portion. Accordingly, a seal structure can be obtained which eliminates the need of, for example, the control of tightening torque and axial force upon fastening, and that facilitates the control of mounting, demounting, and the like of the lid member.